U.S. patent number 7,385,778 [Application Number 11/526,524] was granted by the patent office on 2008-06-10 for control device of storage/reproduction mechanism.
This patent grant is currently assigned to Fujitsu Limited. Invention is credited to Itaru Kakiki.
United States Patent |
7,385,778 |
Kakiki |
June 10, 2008 |
Control device of storage/reproduction mechanism
Abstract
In order to provide a control device for a storage and
reproduction mechanism that can acquire a constant error rate
without being affected by changes of atmospheric pressure, a
control device comprises a storage medium for storing data, a head
for conducting a storage/reproduction process of data on the
storage medium, an error detection unit for detecting an error of
the data read by the head, and a flying height control unit for
controlling a flying height of the head in accordance with the
error rate for correlating changes of the flying height due to the
changes in the atmospheric pressure.
Inventors: |
Kakiki; Itaru (Kawasaki,
JP) |
Assignee: |
Fujitsu Limited (Kawasaki,
JP)
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Family
ID: |
38711739 |
Appl.
No.: |
11/526,524 |
Filed: |
September 25, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070268609 A1 |
Nov 22, 2007 |
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Foreign Application Priority Data
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May 18, 2006 [JP] |
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2006-138711 |
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Current U.S.
Class: |
360/75;
G9B/5.231; G9B/5.033 |
Current CPC
Class: |
G11B
5/09 (20130101); G11B 5/6005 (20130101); G11B
5/40 (20130101) |
Current International
Class: |
G11B
21/02 (20060101) |
Field of
Search: |
;360/75,31,46,294.5
;374/185 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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63-069075 |
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Mar 1988 |
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JP |
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6-236641 |
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Aug 1994 |
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JP |
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11-232812 |
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Aug 1999 |
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JP |
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2002-092810 |
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Mar 2002 |
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JP |
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16-079126 |
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Mar 2004 |
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JP |
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Primary Examiner: Tzeng; Fred
Attorney, Agent or Firm: Greer, Burns & Crain, Ltd.
Claims
What is claimed is:
1. A control device that floats a head for conducting a storage
process or a reproduction process of data on a disk-shaped storage
medium by rotating the storage medium, comprising at least: an
error detection unit for detecting an error from data reproduced by
the head; and a flying height control unit for controlling a flying
height of the head in accordance with the detected error rate,
wherein the control unit compares a predetermined reference error
rate determined in accordance with a desired atmospheric pressure
with the error detected by the error detection unit, determines an
adjustment amount of the flying height of the head in accordance
with a result of the comparison, and adjusts the flying height of
the head by the determined adjustment amount.
2. The control device according to claim 1, wherein the
predetermined reference error rate is measured at a desired
atmospheric pressure.
3. The control device according to claim 1, wherein the desired
atmospheric pressure is an atmospheric pressure to guarantee
operation.
4. The control device according to claim 1, wherein: the flying
height control unit controls the flying height of the head by
changing a flying height control current, the flying height control
current is decreased when the detected error rate is smaller than
the predetermined reference error rate, and the flying height
control current is increased when the detected error rate is larger
than the predetermined reference error rate.
5. A storage device including a control device that floats a head
for conducting a storage process or a reproduction process of data
on a disk-shaped storage medium by rotating the storage medium,
comprising at least: an error detection unit for detecting an error
from data reproduced by the head; and a flying height control unit
for controlling a flying height of the head in accordance with the
detected error rate, wherein the control unit compares a
predetermined reference error rate determined in accordance with a
desired atmospheric pressure with the error detected by the error
detection unit, determines an adjustment amount of the flying
height of the head in accordance with a result of the comparison,
and adjusts the flying height of the head by the determined
adjustment amount.
6. The storage device according to claim 5, wherein the
predetermined reference error rate is measured at a desired
atmospheric pressure.
7. The storage device according to claim 5, wherein the desired
atmospheric pressure is an atmospheric pressure to guarantee
operation.
8. The storage device according to claim 5, wherein: the flying
height control unit controls the flying height of the head by
changing a flying height control current, the flying height control
current is decreased when the detected error rate is smaller than
the predetermined reference error rate, and the flying height
control current is increased when the detected error rate is larger
than the predetermined reference error rate.
9. A control method of floating a head for conducting a storage
process or a reproduction process of data on a disk-shaped storage
medium by rotating the storage medium, causing a storage device to
conduct: an error detection process of detecting an error from data
reproduced by the head; and a flying height control process of
controlling a flying height of the head in accordance with the
detected error rate, wherein the control process compares a
predetermined reference error rate determined in accordance with a
desired atmospheric pressure with the error detected by the error
detection process, determines an adjustment amount of the flying
height of the head in accordance with a result of the comparison,
and adjusts the flying height of the head by the determined
adjustment amount.
10. The control method according to claim 9, wherein the
predetermined reference error rate is measured at a desired
atmospheric pressure.
11. The control method according to claim 9, wherein the desired
atmospheric pressure is an atmospheric pressure to guarantee
operation.
12. The control method according to claim 9, wherein: The flying
height control process is a process of changing a flying height
control current, the flying height control current is decreased
when the detected error rate is smaller than the predetermined
reference error rate, and the flying height control current is
increased when the detected error rate is larger than the
predetermined reference error rate.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control device of a mechanism
that stores and/or reproduces data on a storage medium provided in
a magnetic disc device or the like.
2. Description of the Related Art
Generally, a magnetic disk device is configured in such a way in
which a magnetic head (swing arm) is floated by approximately 0.01
.mu.m to 0.02 .mu.m by means of a stream of air caused by rotating
a magnetic disk at high speed.
Recently, as the density of the recording surface of magnetic disks
has increased, the flying height of magnetic heads have become
increasingly lower.
Accordingly, the magnetic head's flying height is now easier to
affect due to changes in atmospheric pressure, temperature, or
other variations. For example, when the atmospheric pressure
increases, the flying height of the magnetic head also increases,
and, accordingly the signal characteristic deteriorates. When the
atmospheric pressure decreases, the flying height of the magnetic
head decreases in response and the probability that the magnetic
head touches and damages the magnetic disk is greater.
In other words, there has been a problem in which a characteristic
of a signal stored and/or reproduced on the magnetic disk is
affected by the changes of the atmospheric pressure, temperature,
or other variables.
Japanese Patent Application Publication No. 63-069075 discloses a
magnetic disk device that increases the recording surface density
while reducing the risk of impact between the magnetic head and the
disk by decreasing the flying height of the magnetic head only at
times when data is in the process of being stored and/or
reproduced.
Japanese Patent Application Publication No. 06-236641 discloses a
head flying height control device that controls the flying height
of the head of a disk driving mechanism by dynamically adjusting a
read/write head suspension system in real time.
Japanese Patent Application Publication No. 2002-092810 discloses a
magnetic disk device that improves an error recovery ratio by
changing the flying height of the magnetic head in accordance with
error causes.
SUMMARY OF THE INVENTION
The present invention is attained in response to the above problem,
and it is an object of the present invention to provide a control
device for a storage and/or reproduction mechanism that can attain
constant signal quality without being affected by variations of
atmospheric pressure.
In order to attain the above object, the control device according
to the present invention is a control device which floats a head
for conducting a storage process or a reproduction process of data
on a disk-shaped storage medium by rotating the storage medium,
comprising at least an error detection unit for detecting the error
from data reproduced by the head and a flying height control unit
for controlling the flying height of the head in accordance with
the counted error rate.
According to the present invention, even when the flying height of
the head changes due to changes of atmospheric pressure and the
error rate changes, the flying height of the head is controlled in
accordance with the error rate counted by the error detection unit.
Accordingly, a constant flying height can be maintained without
being affected by the change in the atmospheric pressure, such that
the effect is that it is possible to attain a constant signal
quality from the storage and reproduction mechanism.
As explained above, according to the present invention, it is
possible to provide a control device for the storage and
reproduction mechanism that can attain constant signal quality
without being affected by changes of atmospheric pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 explains an outline of a control device according to an
embodiment of the present invention;
FIG. 2 shows a configuration example of a magnetic disk device
according to an embodiment of the present invention;
FIG. 3 explains a reference error rate used for a flying height
control of the magnetic disk device according to an embodiment of
the present invention;
FIG. 4 explains a relationship between an error rate and a flying
height control current Ihr used for the flying height control of
the magnetic disk device according to an embodiment of the present
invention; and
FIG. 5 is a flowchart showing a control process of the flying
height of the magnetic disk device according to an embodiment of
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Herein below, embodiments of the present invention will be
explained, by referring to FIG. 1 to FIG. 5.
FIG. 1 explains an outline of a control device 10 according to an
embodiment of the present invention.
As shown in FIG. 1, the control device 10 according to the present
embodiment comprises at least a storage medium 11 for storing data,
a head 12 for conducting storage/reproduction processes of data on
the storage medium 11, an error detection unit 13 for counting an
error of data read by the head 12, a flying height control unit 14
for controlling a flying height of the head 12 in accordance with
the error rate.
The storage medium 11 is, for example, a magnetic disk of the
storage medium used in a magnetic disk device.
The head 12 conducts storage (write)) and reproduction (read)
processes on data in the storage medium 11 while maintaining a
distance (flying height) which is larger than a prescribed distance
to the storage medium 11. For example, when the storage medium 11
is a magnetic disk, the head 12 is floated with a distance larger
than the prescribed distance by a stream of air caused by rotating
the storage medium 11 at high speed.
The error detection unit 13 counts the error from data reproduced
by the head 12. For example, the error detection unit 13 counts the
error by detecting errors in data from ECC (Error Correcting Code)
assigned to reproduced data.
The flying height control unit 14 compares the error rate counted
by the error detection unit 13 with a predetermined error rate as
reference (hereinafter referred to as "reference error rate"), and
adjusts the flying height of the head 12 in accordance with the
difference between the two.
FIG. 2 shows a configuration example of a magnetic disk device 20
according to an embodiment of the present invention.
The magnetic disk device 20 shown in FIG. 2 comprises at least one
or more magnetic disks 21, a spindle motor 22 for rotating the
magnetic disk 21 at prescribed speed, a magnetic head 23 for
conducting storage and reproduction processes on data in the
magnetic disk 21, a preamplifier 24 for amplifying the signal read
by the magnetic head 23 to a prescribed level, an A/D converter 25
for digitizing the signal read by the magnetic head 23, a
controller 26 for detecting the data error by using the ECC
assigned to the digitized data and calculating an error rate, a MPU
(Micro Processing Unit) 27 for controlling the entirety of the
magnetic disk device 20, a flying height adjustment unit 28 for
adjusting the flying height of the magnetic head 23 in accordance
with the instruction of the MPU 27, a driver 29 for driving the
spindle motor 22 in accordance with the instruction of the MPU 27,
and an I/F 30 which interfaces with the device connected to the
magnetic disk device 20.
When the magnetic disk 21 is rotated at high speed the magnetic
head 23 is floated above the magnetic disk 21 by the stream of air
caused by the rotation. Then, the magnetic head 23 reads the data
stored on the magnetic disk 21, and outputs the read contents to
the preamplifier 24.
The signal, which has been amplified to the prescribed level by the
preamplifier 24, is digitized by the A/D converter 25 and input to
the controller 26. The controller 26 detects data error by using
the ECC assigned to the input data and counts the error. In the
present embodiment, the percentage (%) of erroneous data to the
entire data read is used as the error rate.
The data output from the controller 26 is output to an external
device via the I/F 30.
The MPU 27 calculates an adjustment amount on the magnetic disk 21
based on the difference between the reference error rate and the
error rate counted by the controller 26, and gives an instruction
to the flying height adjustment unit 28.
The flying height adjustment unit 28 floats the magnetic disk 21 by
the adjustment amount instructed from the MPU 27. For example, the
flying height adjustment unit 28, according to the present
embodiment, provides a heat source in the vicinity of the storage
reproduction element of the magnetic head and adjusts the flying
height through thermal expansion of the storage reproduction
element caused by heating it. An electric current controls the
heating by the heat source. Hereinafter, this electric current is
referred to as a flying height control current Ihr. It is to be
noted that the method of adjusting the flying height of the
magnetic disk 21 through thermal expansion is a conventional
method; accordingly, detailed explanations thereof are omitted.
In the above configuration, the storage medium 11 and the head 12
shown in FIG. 1 correspond respectively to the magnetic disk 21 and
magnetic head 23. Also, the error detection unit 13 and the flying
height control unit 14 correspond respectively to the controller 26
and flying height adjustment unit 28.
FIG. 3 explains the reference error rate used for the flying height
control of the magnetic disk device 20 according to an embodiment
of the present invention.
In the present embodiment, in order to acquire the reference error
rate, the error rates of the magnetic disk device 20 at various
altitudes (atmospheric pressures) are measured. FIG. 3 is a graph
showing results of the measurements of the error rates at 6 [kPa],
7 [kPa], 8 [kPa], 9 [kPa], and 10 [kPa].
The magnetic disk device 20, according to the present embodiment,
guarantees operation at an altitude equal to or lower than three
thousand meters above sea level. The atmospheric pressure at the
altitude of three thousand meters above sea level is 7 [kPa];
accordingly, it is assumed that the error rate "a" at the altitude
of 7 [kPa] is the reference error rate.
FIG. 4 explains the relationship between the error rate and the
flying height control current Ihr used for the flying height
control of the magnetic disk device 20 according to an embodiment
of the present invention.
The graph of FIG. 4 shows error rate characteristics based on the
measurement results of the error rates with various flying height.
The flying height is determined by the flying height control
current Ihr, thus, the horizontal axis represents the flying height
control current Ihr.
As shown in FIG. 4, when the flying height control current Ihr
becomes larger, the heat source in the vicinity of the storage
reproduction element of the magnetic head 23 is heated, and the
storage reproduction element is expanded due to the heat;
accordingly, the flying height of the magnetic head 23 becomes
smaller. As a result of this, the error rate becomes lower.
When the flying height control current Ihr becomes smaller, the
heat quantity of the heat source in the vicinity of the storage
reproduction element of the magnetic head 23 becomes smaller, and
the storage reproduction element is less expanded; accordingly, the
flying height of the magnetic head 23 becomes larger. As a result
of this, the error rate becomes higher.
FIG. 5 is a flowchart showing a control process of the flying
height of the magnetic disk device 20 according to an embodiment of
the present invention.
When the magnetic disk device 20 is turned on, the magnetic disk
device 20 is activated, and the process proceeds to a step S501.
Then, in the step S501, the magnetic disk device 20 floats the
magnetic head 23 by rotating the magnetic disk 21 at the prescribed
speed in order to prepare the state in which data can be stored and
reproduced on the magnetic disk 21.
In step S502, the magnetic disk device 20 reads data stored
beforehand on a cylinder on the magnetic disk 21, which is used
only for a flying height measurement, and counts the error rate.
Hereinafter, the above cylinder and the above data are respectively
referred to as "flying height measurement cylinder" and "flying
height measurement data".
Then, the magnetic disk device 20 adjusts the flying height control
current Ihr such that the counted error rate corresponds to the
reference error rate "a" explained in FIG. 3. Hereinafter, the
above adjusted flying height control current is referred to as
"provisional maximum flying height control current Ihmax".
When the adjustment is completed, the magnetic disk device 20
stores the provisional maximum flying height control current Ihmax
on memory (or similar devices) and the process proceeds to step
S503.
In step S503, the magnetic disk device 20 sets (fixes) the flying
height control current Ihr to the provisional maximum flying height
control current Ihmax. In other words, the flying height of the
magnetic head 23 above the magnetic disk 21 is fixed.
In step S504, the magnetic disk device 20 conducts
storage/reproduction processes of data on the magnetic disk 21 in
accordance with the instruction from an information-processing
device or the like connected to the magnetic disk device 20. In
other words, the magnetic disk device 20 conducts read/write
processes of data on the magnetic disk 21.
Also, when retry processes are conducted (because of failures in
reading of data from the magnetic disk 21) the magnetic disk device
20 counts the number of retry processes conducted.
Further, the magnetic disk device 20 detects data errors from the
ECC assigned to the data read by the reproduction process on the
magnetic disk 21 and calculates the error rate.
In step S505, the magnetic disk device 20 checks whether or not the
number of the retry processes counted in the step S504 is equal to
or larger than the prescribed number. When the number of the retry
processes is equal to or larger than the prescribed number, the
magnetic disk device 20 determines that the read error has occurred
too frequently. Then, the process returns to step S502, and the
measurement of the provisional maximum flying height control
current Ihmax is conducted again.
However, when it is determined that the read error has not occurred
too frequently in the step S505, the process proceeds to step
S506.
In step S506, the magnetic disk device 20 compares the error rate
calculated in the step S504 with the reference error rate "a".
Then, if the error rate calculated in the step S504 is lower than
the reference error rate "a", it is determined that the flying
height of the magnetic head 23 above the magnetic disk 21 is
getting smaller, and the process proceeds to step S507. The
magnetic disk device 20 then increases the flying height of the
magnetic head 23 by decreasing the flying height control current
Ihr.
It is possible to prevent a head crash caused by a touch between
the magnetic disk 21 and the magnetic head 23 due to a decreased
flying height of the magnetic head 23.
In the step S506, when the error rate calculated in the step S504
is not lower than the reference error rate "a", the magnetic disk
device 20 causes the process to proceed to step S508.
In step S508, the magnetic disk device 20 compares the error rate
calculated in the step S504 with the reference error rate "a". When
the error rate calculated in the step S504 is higher than the
reference error rate "a" (i.e., when the error rate has risen), the
process proceeds to step S509.
In step S509, the magnetic disk device 20 decreases the flying
height of the magnetic head 23 by increasing the flying height
control current Ihr.
In step S510, the magnetic disk device 20 compares the flying
height control current Ihr and the provisional maximum flying
height control current Ihmax.
When the flying height control current Ihr is equal to or lower
than the provisional maximum flying height control current Ihmax,
the magnetic disk device 20 causes the process to return to step
S504.
When the flying height control current Ihr is higher than the
provisional maximum flying height control current Ihmax, the
magnetic disk device 20 causes the process to proceed to step S511.
Then, the flying height control current Ihr is set to the
provisional maximum flying height control current Ihmax, and the
process returns to step S504.
In step S508, when the error rate calculated in step S504 is not
higher than the reference error rate "a", (i.e., when the error
rate has not risen), the process proceeds to step S512.
In step S512, the magnetic disk device 20 checks whether or not the
current time is an idle time. For example, if a storage and
reproduction process is not conducted on the magnetic disk 21
during a prescribed period, that period of time is determined to be
idle time. When that period of time is determined to be idle time,
the process returns to step S502. When that period of time is
determined not to be idle time, the process returns to the step
S504.
As explained above, by constantly measuring the error rate and
controlling the flying height such that the measured error rate is
always equal to the reference error rate, it is possible to prevent
deterioration of signal characteristics caused by changes of the
flying height due to changes in atmospheric pressure.
In other words, it is possible to control the magnetic head (the
storage and reproduction mechanism) so as to attain a constant
character quality without being affected by changes of the
atmospheric pressure. As a result of this, the number of retry
processes of the magnetic disk device is reduced such that the read
and write processes of data can be accelerated.
It is also possible to prevent a crash caused by the magnetic head
and the magnetic disk touching one another due to the flying height
decreasing due to the lowered atmospheric pressure.
Furthermore, the present invention can be realized simply by adding
a process of controlling the flying height (flying height control
current) by calculating the error rate from the signal reproduced
by the magnetic head; accordingly, it is possible to easily realize
control of the flying height according to the present invention
using a conventional circuit configuration (i.e., without adding a
specialized circuit).
In the above explanation, the present invention has been explained
using examples of magnetic disk device 20. However, the scope of
the present invention is not limited to these examples. The same
effect as in the above embodiments can be attained by applying the
present invention to any storage device that employs a method in
which mechanism conducting storage and reproduction processes of
data on a storage medium is floated by means of rotating the
storage medium at high speed or similar methods.
* * * * *